Based on your comment history you're probably just being sarcastic.
That said, I agree with your point even if you probably don't: using the wrong word in the wrong place is not a good thing. Conflating copyright infringement with theft is bad even if you empathize with the person whose copyright was infringed.
You could presumably define "theft" as owning something without paying the price that has been set for it (in this case, infinity). The bottom line is that you're using this word to talk about a type of ownership which you've judged to be a social ill. Despite what RMS may say, it seems reasonable to associate this with the historical judgments about ownership that are tied up with the word "theft".
Also, we need to expand the meaning of words by analogy, otherwise we're left with calling things Thing A and Thing B.
You could define it like that, but you wouldn't be entirely correct. Depriving the original owner of whatever is stolen is innate in the concept of "theft"[1][2]. That is the primary reason society has had laws against theft for so long--not because we're afraid of everybody having a pony, but because my stealing a pony deprives its original owner of it.
Since copyright infringement does not stop the original "owner" from using the property in question, calling it theft seems intellectually dishonest. All the historical judgments are based around this idea--the reason theft is inherently bad and punished by so many societies is that the person stolen from does not have use of his property any more. Extending these to something that does not deprive the original owner of anything is not reasonable.
Besides, the idea of "owning" information involves having exclusive control over its distribution. Given this parallel, somebody just having an unauthorized copy does not own the information as they have no exclusivity or control over it whatsoever. If somebody with such a copy could then enforce that others could not use the information, it would be akin to owning it, but it would also be a very different story!
So your definition of theft would probably have to be amended to "using something without paying the price..." since just having a copy of something confers no ownership. But then this definition suddenly becomes very broad--much more broad than the commonly accepted meaning of theft. For example, trespassing would fall under "theft" as you're using somebody's land without their permission or "paying the price".
Expanding words by analogy is a good thing, granted. However, this assumes that the analogy is reasonably accurate. There are clearly harmful examples of expanding words by poor analogy: the oft-repeated mantra that "evolution is just a theory" only exists because the analogy between the common use of "theory" and the scientific use is fundamentally flawed.
So expanding words' meanings by analogy is good assuming the analogy is not relatively misleading or clearly biased. The analogy between theft and copyright infringement is both, so this use should not be encouraged.
If I had my way the usage of analogies and semantic bickering would be strictly forbidden in threads pertaining to copyright infringement. There is a real discussion to be had about the situation at hand, but instead the top sub-thread is the exact same circle jerk that happens in every other copyright related thread.
I wonder how long we have until someone makes a car analogy?
That said, I agree with your point even if you probably don't: using the wrong word in the wrong place is not a good thing. Conflating copyright infringement with theft is bad even if you empathize with the person whose copyright was infringed.